Apatite-containing glass ceramics and apatite sintered ceramics are known and are, e.g., described in DD 219 017 and in DD 245 864. Such biomaterials form direct bonds to living bones.
However, as an inorganic component in ionomer cements, special requirements are made of a glass ceramic. Apatite-containing glass ceramics for glass ionomer cements have not yet been developed. Glass ionomer cements are formed by mixing fluoroalumosilicate glass powder with polymeric carboxylic acids. Glass ionomer cements are used in stomatology for suitable indications such as underfilling, stump reconstruction and securing.
A combination consisting solely of fluoroalumosilicate glass powders and polyacrylic acid gives glass ionomer cements with poor processing properties. The glass ionomer cement takes too long to set completely, so that its surface becomes brittle as a result of contact with saliva in the mouth of the patient. To overcome these disadvantages the Japanese Patent 52 (1977) 101 893, for example, discloses an aqueous polyacrylic acid or acrylic polymer solution, which contains one or more polybasic carboxylic acids. By using this liquid, shorter setting times and greater mechanical strengths are achieved. U.S. Pat. No. 4,360,605 discloses a hardening liquid which contains, in addition to an acrylic acid copolymer, tartaric acid. It was ascertained that with this the ratio of processing time to setting time was further improved. With glass ionomer cements the processing time should be long and the setting time as short as possible. In this respect, these glass ionomer cements still do not fulfil the requirements of the user.
With glass ionomer cements the setting process is characterized by the formation of calcium and aluminium polycarboxylates. In the first reaction step a still relatively water-sensitive calcium polycarboxylate forms, and only the formation of aluminium polycarboxylate, which takes place later due to its higher degree of order and the lower migration speed of the more highly-charged aluminium ions, leads to a stable cement system. Fluoroalumosilicate glass powders of the SiO.sub.2 --Al.sub.2 O.sub.3 --CaO--P.sub.2 O.sub.5 --Na.sub.2 O--F.sup.- system according to U.S. Pat. No. 4,376,835 have the disadvantage that bending strength and adhesion on the hard dental substance are inadequate. According to Wilson and Mclean [Glass Ionomer Cement, Quintessenz-Verlag Berlin (West) 1988, 28], the function of the calcium ions in the setting process can be taken over by strontium ions. Strontium-containing fluoroalumosilicate glass powders according to DE-A 3 804 469 admittedly show improved properties with regard to solubility and X-ray visibility, but display insufficient bending strengths and adhesion on the hard dental substance.
Wilson and colleagues (Ind. Eng. Chem. Prod. Res. Dev. 19, 1980, 263-270) investigated glasses in which CaF.sub.2 crystals formed in a secondary process. It was ascertained that these glasses have a lower mechanical strength than the corresponding clear glasses.